Twins discordant for vater association. Obstructed labor of the second twin due to ascites and persistent cloaca without communication to the exterior.

The unusual delivery of a dead second twin with rare malformations is presented. The first twin, born live following a normal labor, had no malformations. The birth of the second twin was obstructed by massive ascites, and its abdomen had to be perforated before delivery. The sex could not be determined due to lack of the internal genitalia and the fetal appearance of the external genitals. The left kidney and ureter were hypoplastic. The right ureter and distal part of the colon were dilated and opened into a large primitive cystic cloaca without communication to the exterior. The ascites was probably caused by the urinary obstruction. These malformations probably represent one of the earliest arrested developments of the embryonic hindgut. The presence of a tracheo-esophageal fistula and a single umbilical artery, together with the anal atresia and the renal anomalies, could indicate that the anomalies formed part of the VATER association.